yep edward is right
wd40 will contaminate the switch and then dirt will cause it to start sticking again.
Brake cleaner will dry out the oil in the bakolite material the switch is made of and make it extremely brittle. That goes for plastic/nylon parts as well.

The only thing any tech should be using to clean electrical components with is pressurized air or some type of electrical cleaner that is fast evaporating and preferably non-flammable, but I've found the non-flammable brands don't work quite as well. You just have to use air and dry the part off before applying current to it is all :o)

But i think you have located the culprit, by spraying something on them and the truck started working correctly tells the story.
If it were me i'd order new switches and replace those old sticky ones. ;o)